The prior art has proposed a variety of mechanisms for generating and packaging flexible medical tubing. Various types of cutters, for example, have been used in cutting and collection processes. Many systems employ a manual method for monitoring the tubing diameter of cut tubing, by manually measuring the tubing diameter of samples taken at periodical intervals and analyzing these measurements using statistics. These manual methods are subject to error, since momentary variations in diameter may occur, for example. Momentary variations in diameter, resulting from momentary disruptions in a previous extrusion process, may be missed altogether by manual sample taking methods. Other approaches for monitoring the tubing diameter have incorporated laser measurement techniques, which may be programmed to shut the tube cutting machine down or to sound a buzzer when a tubing diameter is out of specification.
In addition to controlling the diameter of cut tubing portions, the prior art has also endeavored to control the length of these cut tubing portions. One method used by the prior art utilizes a pulse generator, which is driven by frictional contact with the moving cut tube portions. Pulses from the pulse generator provide an indication of movement length of the cut tube portion, for any given time period. By calibration of time interval pulse counts and lengths generated and measured by hand, approximate tubing lengths can be "dialed" into the operation by the machine operator. Corrections for machine speed and shrinkage variations may also be made.
One problem associated with this method results from slippage between the tube product and the pulse generator drive wheel. This slippage may introduce errors in the measured tubing length. Several attempts have been made by the prior art to automate the length control, and to compensate for machine speed variations. U.S. Pat. No. 4,585,600 uses the counting and storage of generated pulses between when the forward end of a cut propellant passing in sequence between two sensors as means for signalling a cutter. U.S. Pat. No. 3,406,601 uses a product movement-actuated-pulse-generator and at least one downstream sensor to actuate a cutter. Errors are minimized by further downstream checkpoints and feedback.
While these prior art approaches have been somewhat successful, an efficient and reliable length measuring device that is independent of slippage has not yet been developed. Additionally, a fully automated system for measuring cut tube portion diameters and lengths, and for feeding this data to a statistical controller, has not been developed. Nor has the prior art developed a controller for utilizing statistical data for sorting unacceptable cut tubing portions from acceptable cut tubing portions, and for generating certification printouts for each batch of cut tubing portions.